Impregnated electrical contact brush and method of producing the same



2,754,231 Patented July 10, 1956 HVIPREGNATED ELECTRICAL CONTACT BRUSH high concentrations of barium carbonate are desired, or when solutions containing a small percentage of the soluble salt are used, multiple impregnations may be necessary to introduce suflicient barium carbonate into the brush.

AND METHOD OF PRODUCING THE SAME 5 The stock is then placed in hydrofluoric acid saturated with barium fluoride, washed and heated. The resin im- Dimiter h and Crelght? Jones pregnation is achieved by impregnating the stock, at re- Rohky Rlver f asslgnors g g 3; and duced and increased pressures, in a volatile solvent solu- Carbon Corpommm a corpora on o ew or tion of resin. The solvent is then removed by reduced No Drawing. Application August 5, 1953, pressure and heat, packed in coke and heated to coke the Serial No. 372,610 resin. This step is required to bind the barium fluoride to the carbon to prevent dusting at high altitudes. An 11 Chums (CL 117-416) alternative method is to fire the brush directly, not packing it in coke. The amount of coke retained in the brush This invention relates to an electrical contact brush of 15 depends on the amount of resin introduced t the ru the type generally used on motors and generators. More P i the manner in Which it is eokedp particularly, the invention relates to an electrical contact P h 1h e and heatlhg slowly t 400 the Coke brush, and the method of preparation thereof, which has retained for a glveh amohht of Teen} 1S gfeatest- The e exhibited excellent operating properties at high altitudes of elther method of behdlhg the barium fillollde results 111% as well as at sea levei 0 a suflicient bonding to prevent brushes from dusting at a The performancg of conventional glectrical ontact simulated altitude Of up sixty thousand fefit. be brushes made of carbon or graphite is known to be affected hhflerstbbd that he reslhe can be Used. the .reqlhremeht to a considerable extent by atmospheric conditions. A belhg thelr caPebIhtY of e ng e Exp r men s a brush which is iI1 every way satisfactory at sea level shown that both thermosetting res1ns, for example, phenolder normal conditions will often prove to be inoperable formaldehyhe Teslhs h thermoplastle reslhs, e p at altitudes of several thousand feet above sea level. chhtharohelhhehe teslhs, h protilleed the desired e- Many brushes disintegrate, or dust as it is descriptively The shififie pr gnation, the final step, 18 referred to, at altitudes easily obtainable with todays air- F h by lmpreghahhg the treated Stock With qh craft. This behavior is believed to be attributable to the Sliver httrate and elevated Pressures, i g 1n paucity of oxygen and water vapor at these altitudes since water and plhclhg ammohlum hydrosulfide to oxygen and water contribute to the formation of a film on hohvert the hthhte to Sulfide, followed by y g, P g the surface of a commutator. A film on which the brush 1h Coke and h rides is essential to proper commutation and brush per- The q q treatment 13 ah f e of the Preferred formance manner in which brushes of the invention may be pre- The prior art teaches the addition of certain materials pared} Electmgraphlhc brush e i Suitably in the Shape to carbon or graphite brushes to improve their operating and Sue of thehhlshbd h l 1S Placed 111311 q h s properties Metals such as Silver and copper have been saturated solution of barium acetate, the impregnation added to change the resistance of the brush and to lower belhg earned out at redhceh and Increased PressureS the contact drop between the brush and the commutator. 30 Hg and 90 of 5 hhhhtes The other additives have been used to alter or form a film on 40 stock is then heated to about 650 C. for about 5 minutes, the surface of a commutator. Some treatments which are thus decomposlhg the barium acetate to t barium excellent for brushes to be used at high altitudes render f The stohk so treated 15 then Introduced nt a them ti f t for operating at sea 1 The container of barium fluoride saturated hydrofluoric acid verse is also mm until the evolution of carbon dioxide ceases, usually about The principal object of the present invention is to pro- 1 hours, converting the barium carbonate to barium fluovide an electrical contact brush with .generally improved Tide, tehewed y Washing Wi h Water for four hours and operating properties. Another and more specific object then heating at 150 C. to drive oil? the water and residual of the invention is to provide an electrical contact brush hydwfihone acld- H which gives excellent service at high altitudes. so The banufh h e lhlpleghated t k is hen im- The objects of the invention are accomplished by inpregnated with tne resin as follows: The stock is placed eluding in a conventional carbon or graphite brush a m a sohlhoh of Part, y g of a P o -formaldecompound of an alkaline earth metal and a compound of y e to eight p y weight, of acetone, the silver bonded in and to the brush by means of a coked Preghatloh taking Place at 21 in. following Which the resin. 5 stock is air dried for about 16 hours and then pumped The preferred embodiment of the invention is an elec- 5 at 29-30 in. Hg for two hours to remove any residual tro-graphitic brush containing barium fluoride and silver acetone. The stock is then heated for two hours at 150 sulfide bonded to the brush by a coked phenolic resin. C. to cure the resin, packed in coke and heated for six Best results have been obtained with an electrographitic hours at 400 C. to 700 C. to partially coke the resin. brush containing about seven to nine percent, by weight, The final treatment is vacuum-pressure impregnation of barium fluoride, bonded to the brush by a coked resin with a 25%, by weight, aqueous solution of silver nitrate, (about 0.1 to one percent, by weight), and about one 'to after which the stock is rinsed in water, and placed in a three percent silver-silver sulfide. This brush has exhibicontainer of 8 to 12% ammonium hydrosulfide soluted excellent ebmmhtatihg Properties at Sea e l nd at tion and soaked for 16 hours converting the silver nitrate simulated altitude conditions up to 60,000 feet. to silver sulfide.- The stock is then removed, oven dried The means whereby the objects of the invention are for o h at 150 (3 packed in coke and heated for achieved comprise impregnating suitably shaped and sized two hours at 400 C. to 700 C. This completes the electrographitic brush stock in a saturated aqueous solubrush treatment. tion of barium acetate at reduced and increased pressures The brushes as prepared in the foregoing example perfollowed by heating to decompose the acetate to carformed satisfactorily on a motor operating at 6500 revobonate. Aqueous solutions of other salts, which decompose on heating to yield barium carbonate, can be employed to impregnate the brushes of the invention. When lutions per minute while carrying a current density of amperes per square inch in an atmosphere simulating conditions up to sixty thousand feet above sea level.

The brush stock which is impregnated to make the brush of the invention can be any of the conventional carbonaceous materials conventionally employed in the making of brushes. Carbon flour, lamp-black, and graphite, both natural and artificial, are examples of such carbonaceous materials. In the appended claims the term carbonaceous brush stock includes all of the conventional brush forming material.

The composition and the method of its achievement were substantially disclosed but not claimed in that patent application by M. T. McCrary et al. entitled Electrical Contact Brush, Serial No. 302,246, filed August 1, 1952.

What is claimed is:

1. An electrical contact brush comprising carbonaceous brush stock and containing from 5% to 12%, by weight, of a compound of an alkaline earth metal bonded therein and thereto by a coked resin, and containing from 0.5% to by weight, of a water-insoluble silver compound.

2. An electrical contact brush comprising carbonaceous brush stock and containing from 5% to 12%, by weight, of a compound of an alkaline earth metal and containing from 0.5% to 10%, by weight, of a waterinsoluble silver compound, bonded therein and thereto by a coked resin.

3. An electrical contact brush comprising carbonaceous brush stock and containing from 5% to 12%, by weight, of a compound of an alkaline earth metal bonded therein and thereto by a coked, heat-hardenable, thermosetting, phenol-formaldehyde resin, and containing from 0.5% to 10%, by weight, of a water-insoluble silver compound.

4. An electrical contact brush comprising carbonaceous brush stock and containing from 5% to 12%, by weight, of a compound of an alkaline earth metal and containing from 0.5% to 10%, by weight, of a water insoluble silver compound, bonded therein and thereto by a coked, heat-hardenable, thermosetting, phenol-formaldehyde resin.

5. An electrical contact brush comprising carbonaceous brush stock and containing from 5% to 12%, by weight, of barium fluoride bonded therein and thereto by a coked, thermoplastic, coumarone-indene resin, and containing from 0.5 to 10%, by weight, of silver sulfide.

6. An electrical contact brush comprising carbonaceous brush stock and containing from 5% to 12%, by Weight, of barium fluoride, and containing from 0.5 to 10%, by weight, of silver sulfide, bonded therein and thereto by a coked, thermoplastic, coumarone-indene resin.

7. An electrical contact brush comprising carbonaceous brush stock and containing from 5% to 12%, by weight, of barium fluoride bonded therein and thereto by a coked, heat-hardenable, thermosetting, phenol-formaldehyde resin, and containing from 0.5% to 10%, by weight, of silver sulfide.

8. An electrical contact brush comprising carbonaceous brush stock and containing from 5% to 12%, by weight, of barium fluoride, and containing from 0.5 to 10%, by weight, of silver sulfide, bonded therein and thereto by a coked, heat-hardenable, thermosetting, phenol-formaldehyde resin.

9. A method of producing a carbonaeous electrical contact brush containing a compound of an alkaline earth metal bonded therein and thereto by a coked resin and containing silver sulfide, which method comprises impregnating such brush with an aqueous solution of an alkaline earth metal compound; converting said alkaline earth metal compound to an insoluble alkaline earth metal compound by heating; introducing into said brush, in volatile solvent solution, about 11 per cent by weight of a resin capable of being coked; heating said brush, thus removing said solvent and coking said resin; introducing silver nitrate in aqueous solution into said brush; converting said silver nitrate to silver sulfide; drying, packing in coke and heating said brush at a temperature in the range from 400 C. to 700 C.

10. A method of producing a carbonaceous electrical contact brush containing 5% to 12% barium fluoride bonded therein and thereto by a coked resin and containing 0.5 to 10% silver sulfide, which method comprises impregnating such brush with an aqueous saturated solution of barium acetate by vacuum-pressure means; converting said barium acetate to barium carbonate by heating; converting said barium carbonate to barium fluoride with hydrofluoric acid; impregnating said brush at reduced pressure with an 11%, by weight, solution in acetone of a heat-hardenable, thermosetting, phenolformaldehyde resin; heating said brush at a temperature in the range from C. to 200 C. for a period of time sufficient to set the resin; packing said brush in coke; heating said brush from 5 to 7 hours at a temperature in the range from 400 C. and 700 C.; impregnating said brush at reduced pressure with a 25%, by weight, aqueous solution of silver nitrate; converting said silver nitrate to silver sulfide with ammonium hydrosulfide; drying said brush; packing said brush in coke; heating said brush from IV: to 2% hours at 400 C.

11. In an electrical contact brush composed of carbonaceous brush stock, and containing as impregnants, an alkaline earth metal compound and a Water insoluble silver compound, the improvement which comprises said impregnants being bonded to and in said brush stock by coked resin, whereby said impregnants are retained in said stock under extreme operating conditions.

References Cited in the file of this patent UNITED STATES PATENTS 1,856,680 Williams et a1 May 3, 1932 2,428,036 Peters et a1 Sept. 30, 1947 2,530,984 Moberly Nov. 21, 1950 

1. AN ELECTRICAL CONTACT BRUSH COMPRISING CARBONACEOUS BRUSH STOCK AND CONTAINING FROM 5% TO 12%, BY WEIGHT, OF A COMPOUND OF AN ALKALINE EARTH METAL BONDED THEREIN AND THERETO BY A COKED RESIN, AND CONTAINING FROM 0.5% TO 10%, BY WEIGHT, OF A WATER-INSOLUBLE SILVER COMPOUND. 